1. Field of the Invention
The present invention relates to an image pickup optical system and an image pickup apparatus using the same.
2. Description of the Related Art
In recent years, with a thinning of equipments such as a mobile telephone, a portable terminal, and a personal computer, a camera module in which, a length of an optical system in an optical axial direction is thinned to the minimum has been sought. In order to fulfill the requirement, a large number of optical systems with a single focal length, which include about two to three aspheric lenses, have been proposed.
Moreover, in recent years, with the technological development of an image pickup element and the increasing needs of the market, a camera module which is small as well as has a large number of pixels, wide angle, and low-cost, has been sought. As an optical system in which, shortening of an overall length of the optical system is facilitated while improving an image forming performance, an optical system proposed in Japanese Patent No. 4317933 and optical systems proposed in Japanese Patent Application Laid-open Publication Nos. 2008-268946 and 2009-169005, in which, the number of lenses is let to be four, are available.
These optical systems use four lenses and correct a chromatic aberration favorably for improving a resolution for a large number of pixels while having a small size.